The present invention relates to a hydraulic control apparatus for an automatic transmission which controls a gear ratio on the basis of a vehicle speed estimating value after a predetermined elapsed time.
Conventionally, there has occurred the following problem in the art. When a second shift is determined during performing a first shift, that is, when a first shift and a second shift are sequentially performed (hereinafter referred to as sequential shift), it takes a long time until a final speed is achieved if the second shift is performed after termination of the first shift. In order to solve this problem, there has been proposed Japanese Patent Application First Publication No. 9-273627 that discloses a control apparatus for an automatic transmission. Immediately after the second shift is determined during performing the first shift, the controller outputs a hydraulic command to bring a friction element into engagement upon the second shift, and the second shift is started after a predetermined time elapsed from the output of the hydraulic command on the assumption that a piston stroke of the friction element is accomplished.
In addition, Japanese Patent Application First Publication No. 4-60271 discloses a hydraulic control apparatus for a transmission that is adapted to suppress occurrence of interlock between a first friction element and a second friction element upon simultaneous engagement thereof. The hydraulic control apparatus includes a selector valve in a hydraulic circuit for the second friction element that causes rapid reduction when brought into engagement simultaneously with the first friction element. The selector valve is operative to block supply of a working oil to the second friction element when the first friction element is in the engagement state.